In general, an air conditioner for a vehicle includes a cooling system for cooling the interior of the vehicle and a heating system for heating the interior of the vehicle. At an evaporator side of a refrigerant cycle, the cooling system converts air into cold air by heat-exchanging the air passing outside an evaporator with refrigerant flowing inside the evaporator so as to cool the interior of the vehicle. At a heater core side of a cooling water cycle, the heating system converts air into warm air by heat-exchanging the air passing outside the heater core with cooling water flowing inside the heater core so as to heat the interior of the vehicle.
Moreover, a hybrid vehicle which is operated by an engine (internal combustion engine) and an electric motor uses waste heat (cooling water) of the engine as a heat source for heating the interior of the vehicle.
That is, the hybrid vehicle uses the air conditioner for heating in the same way as the conventional vehicles because the waste heat of the engine is sufficient when the vehicle is operated by the engine, but uses the remaining heat of engine cooling water as the heat source even though the engine is turned off when the vehicle is operated by the electric motor.
In the case that the vehicle is operated by the electric motor, if outdoor temperature is low (below zero), the vehicle cannot be operated by the electric motor due to a lack of the remaining heat of the engine cooling water when the engine cooling water is below a predetermined temperature. However, the engine is forcedly operated in order to secure the heat source for heating, such that the fuel efficiency of the hybrid vehicle is deteriorated.
In order to improve the fuel efficiency of the hybrid vehicle at low temperature, air conditioners to each of which a heat pump system is applied have been developed.
FIG. 1 illustrates an example of a conventional heat pump system for a vehicle. As shown in FIG. 1, the heat pump system for the vehicle includes: a compressor 30 for compressing and discharging refrigerant; an interior heat exchanger 32 for radiating heat of the refrigerant discharged from the compressor 30; a first expansion valve 34 mounted in parallel for selectively expanding the refrigerant passing through the interior heat exchanger 32; an exterior heat exchanger 48 for heat-exchanging the refrigerant passing through the first expansion valve 34 outdoors; an evaporator 60 for evaporating the refrigerant passing through the exterior heat exchanger 48; an accumulator 62 for dividing the refrigerant passing through the evaporator 60 into a gas-phase refrigerant and a liquid-phase refrigerant; a second expansion valve 56 for selectively expanding the refrigerant supplied to the evaporator 60; and a bypass line 58 for making the refrigerant passing through the exterior heat exchanger 48 bypass the second expansion valve 56 and the evaporator 60 in a heat pump mode.
The evaporator 60 and the interior heat exchanger 32 are respectively mounted inside an air-conditioning case 50, and in this instance, a heater core 70 is mounted between the evaporator 60 and the interior heat exchanger 32 inside the air-conditioning case 50.
Cooling water of an engine 72 is circulated inside the heater core 70, and a temperature adjustable door 74 adapted for adjusting a mixed amount of cold wind and warm wind is mounted between the evaporator 60 and the heater core 70.
The conventional heat pump system for the vehicle having the above-mentioned structure, in the heat pump mode (the maximum heating mode), the refrigerant discharged from the compressor 30 passes through the interior heat exchanger 32, the first expansion valve 34, the exterior heat exchanger 48, the bypass line 58, and the accumulator 62 in order, and then, is returned to the compressor 30. In this instance, the interior heat exchanger 32 serves as a heater and the exterior heat exchanger 48 serves as an evaporator.
Therefore, in the heat pump mode, the heat pump system carries out heating using the interior heat exchanger 32 under the condition that the vehicle is operated by the electric motor, but carries out heating using the heater core 70 in which the cooling water of the engine 72 circulates under the condition that the vehicle is operated by the engine, so as to enhance fuel efficiency.
In the meantime, in an air-conditioning mode (the maximum cooling mode), the refrigerant discharged from the compressor 30 passes through the interior heat exchanger 32, the exterior heat exchanger 48, the second expansion valve 56, the evaporator 60, and the accumulator 62 in order, and then, is returned to the compressor 30. In this instance, the interior heat exchanger 32 which is closed by the temperature adjustable door 74 serves as a heater like in the heat pump mode, and the evaporator 60 serves as a cooler.
However, in case that the conventional heat pump system for the vehicle is applied in order to enhance fuel efficiency at low temperature, because the waste heat of the engine 72 and the heat pump system are used together, the interior heat exchanger 32 which is a heat exchanger for a heat pump is added inside the air-conditioning case 50, and hence, it is difficult to use the air-conditioning case 50 commonly and manufacturing costs are increased due to an increase in size and weight of the air-conditioning case 50.